[Grammar] .....seeing various landmarks

[Ook Choi]

The browse interface allows users to move gradually through a site, seeing various landmarks as they pass through the site hierarchy.

Hi, I would like to grammatically understand this sentence. What is subject of verb seeing? is there any omission
before seeing? (i.e. they(or who) are seeing various...)

1. why has it been omitted?
2. why ONE long sentence? I think we can break it to two sentence but I have seen a lot this kind of structure.
when does this kind of structure use? (i.e. when can I omit like that?)

 

[Odessa Dawn]

​

Good question! I have the same problem with that.

Have a look pleas!

They are in fact angels, coming to tell Sarah that she will have a child. No subject/verb.

More: Even Higher Than Angels - Covenant & Conversation - Parsha

 

[Ook Choi]

Ya... apparently there are omission ....who is..
but I dont know when it can be omitted....